Donald Sutherland, who wore a prosthetic nose and chin, shaved off the front part of his hair, once telling a laughing crowd "When Fellini says get a hair cut, you get a hair cut."
Federico Fellini had to re-shoot parts of this movie, including the elaborate Venice carnival scene, when several reels of film were stolen at the Technicolor labs of Rome, on August 17, 1975. Some reels of Pier Paolo Pasolini's Salò, or the 120 Days of Sodom (1975) and Damiano Damiani's spaghetti western A Genius, Two Partners and a Dupe (1975) were also stolen. Apart from the re-shoots, this theft also forced Fellini to abandon a sequence featuring Barbara Steele. The negatives were found again in May 1976.
In an interview, Federico Fellini explained why he chose Donald Sutherland to play Casanova, "It seemed to me that Donaldino's [Sutherland] face was perfectly adapted to the image of an Italian who was unripe, juvenile, a kind of Pinocchio-in-the-uterus, which was the image I had of the real Casanova whom I considered a stronzo or fool, an idiot. Only a great professional actor like Sutherland could incarnate such negative qualities effectively. In addition, Don has fabulous blue eyes. As my Casanova, these eyes expressed the sterile masturbatory fantasies of the voyeur, of a walking sperm bank suffering from chronic insomnia."
Discussing his role in the Getty-kidnap TV drama Trust (2018), Donald Sutherland recalled filming Casanova in Italy during this period of high-profile kidnappings by the Mafia. He had to be driven to and from the studio wearing a white bag on his head to preserve his anonymity, and later discovered that the producer had bought kidnapping insurance for him but did not tell him at the time as that was a condition of the policy.
The sea in the film was created from cut-up black trash-bags; Federico Fellini wanted to put high emphasis on the plasticity of Casanova's life and journey.